Numerical evaluation of virtual corrections to multi-jet production in massless QCD

Abstract

We present a C++ library for the numerical evaluation of one-loop virtual corrections to multi-jet production in massless QCD. The pure gluon primitive amplitudes are evaluated using NGluon (Badger et al., (2011) [62]). A generalized unitarity reduction algorithm is used to construct arbitrary multiplicity fermion–gluon primitive amplitudes. From these basic building blocks the one-loop contribution to the squared matrix element, summed over colour and helicities, is calculated. No approximation in colour is performed. While the primitive amplitudes are given for arbitrary multiplicities, we provide the squared matrix elements only for up to 7 external partons allowing the evaluation of the five jet cross section at next-to-leading order accuracy. The library has been recently successfully applied to four jet production at next-to-leading order in QCD (Badger et al., 2012 [92]). Program SummaryProgram title:NJetCatalogue identifier: AEPF_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPF_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: GNU General Public License, version 3No. of lines in distributed program, including test data, etc.: 250047No. of bytes in distributed program, including test data, etc.: 2138947Distribution format: tar.gzProgramming language: C++, Python.Computer: PC/Workstation.Operating system: No specific requirements — tested on Scientific Linux 5.2. and Mac OS X 10.7.4.Classification: 11.5.External routines: QCDLoop (http://qcdloop.fnal.gov/), qd (http://crd.lbl.gov/dhbailey/mpdist/), both included in the distribution file.Nature of problem:Evaluation of virtual corrections for multi-jet production in massless QCDSolution method:Purely numerical approach based on tree amplitudes obtained via Berends–Giele recursion combined with unitarity method.Restrictions:Full colour and helicity summed corrections only up to 5 final state jets.Running time:Full colour and helicity summed 2→4 channels take around 0.5–8 s per point depending on the number of fermion lines. Realistic times obtained during Monte Carlo integration will be highly dependent on the specific application.